And if your longer race is at a faster pace, the calculator gets wonky...and assumes you will get faster the longer the race is.

If I put in my marathon PR and my 11.11 mile trail race PR (yes, it was really that distance), I get hilarious results because the shorter race was at a slower pace. It uses that time-created coefficient to predict how much your performance will decay as your distance increases. That coefficient only works if you ran the shorter race faster.

"When a person trains once, nothing happens. When a person forces himself to do a thing a hundred or a thousand times, then he certainly has developed in more ways than physical. Is it raining? That doesn't matter. Am I tired? That doesn't matter, either. Then willpower will be no problem." Emil Zatopek

And if your longer race is at a faster pace, the calculator gets wonky...and assumes you will get faster the longer the race is.

I think that explains it, thanks. I did a decently speedy long run and plugged it in for race 1 and then tried various recent shorter distance runs (which are all slower) for race 2 and kept seeing way-too-good marathon predictions...

I think that explains it, thanks. I did a decently speedy long run and plugged it in for race 1 and then tried various recent shorter distance runs (which are all slower) for race 2 and kept seeing way-too-good marathon predictions...

Why would you assume that any calculator could automatically adjust for idiosyncratic and arbitrary times?

The instructions for this calculator, its method of computation, and its limits are all pretty clearly spelled out in the instructions on the page of the calculator.

Why would you assume that any calculator could automatically adjust for idiosyncratic and arbitrary times?

The instructions for this calculator, its method of computation, and its limits are all pretty clearly spelled out in the instructions on the page of the calculator.

No, I did not expect the calculator to be magical. It was certainly user error and I'm grateful it was pointed out and explained. I do not race much so I don't really have race times to put in, so I put in recent training times. The example I provided did not start out as arbitrary, it was the result of my fiddling with the numbers after failing to make sense of results based on training run times that I put in (which didn't work out correctly because of the reason rgilbert explained).

No, I did not expect the calculator to be magical. It was certainly user error and I'm grateful it was pointed out and explained. I do not race much so I don't really have race times to put in, so I put in recent training times. The example I provided did not start out as arbitrary, it was the result of my fiddling with the numbers after failing to make sense of results based on training run times that I put in (which didn't work out correctly because of the reason rgilbert explained).

Okay, but actually it didn't work out correctly for a different reason.

Yes, that and because (at least in the example that you showed) the races were the same distance. You need to choose two "all out" races, of different distances, run at approximately the same fitness level.

Of course, even then it's a crap shoot because it's just a calculator.

Yes, that and because (at least in the example that you showed) the races were the same distance. You need to choose two "all out" races, of different distances, run at approximately the same fitness level.

Of course, even then it's a crap shoot because it's just a calculator.

It started out with me putting in my latest run on 9/9 @ 8:49 pace (which while not a race, it was a decent effort run). Then I put in a training run time from the past 2 weeks for "race 2". It turned out all my training runs from the last 2 weeks were run at slower pace, and all but 1 were of shorter distance. When I couldn't get the result to make sense (I was getting marathon predictions closer to 3 hr), I started trying to debug what went wrong, leading to the example I showed hoping to highlight the problem. (In my mind somehow I thought 2 similar racetime data should converge better to a more accurate result, but it didn't)

It seems it's not easy to get even a ballpark figure for a future race unless I race often, but if I race often I probably wouldn't need a calculator to help me decide at what pace I should race at...